JPS61235072A - Production of aluminum heat exchanger - Google Patents

Abstract

PURPOSE:To make a heat exchanger light-weighed and to increase the corrosion resistance by coating Zn-Al alloy layer on the perforated tube side for refrigerant circulation, by bending said tube in meandering shape at either before or after this coating and by joining the corrugated fin. CONSTITUTION:In the production of the heat exchanger of the capacitor for the air conditioner on vehicle the Al or Al alloy made perforated flat tube 1 of the sectional shape shown in the figure is formed by extrusion work. The tube 1 is fed to a flux device A, a flux 6 is coated on the surface thereof and is fed to a hot dipping device C after preheating by a preheating device B. Now the Zn-Al alloy 3' heated beyond the melting point is hot-dipped to the tube 1. The tube 1 of which surface is coated by this Zn-Al alloy layer 3 is bent in meandering shape, a fin 2 is inserted between the parallel part thereof and after fixing and holding by the jig the same flux as the above is coated on this assembly body, which is then heated inside a heating furnace and the tube 1 and fin 2 are joined by melting the layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing an aluminum heat exchanger used in a condenser, evaporator, etc. of a vehicle-mounted air conditioner.

(Prior Art) In the automobile industry, where improving fuel efficiency by reducing vehicle weight is an important technical issue, measures to reduce the weight of heat exchangers for in-vehicle air conditioners are also being sought. The general manufacturing method for this type of heat exchanger, such as a condenser or evaporator, is to first bend an extruded aluminum alloy multi-hole tube for refrigerant flow into a serpentine shape to form the main body, and then Insert into the gap between the tubes an extremely thin aluminum alloy corrugated fin with a wall thickness of about 0.16 mm, the surface of which has been clad with brazing filler metal, and use a jig to create this combined structure. A method has been adopted in which the assembly of the tube and fin is completed by brazing by holding the entire tube in a heating furnace and heating it to the melting temperature of the brazing filler metal.

The material for the fins is an aluminum alloy whose electrode potential is less noble than that of the tube material. Under conditions where corrosion is likely to occur, the fins corrode before the tube, which is a so-called sacrificial corrosion effect. The idea was to improve the corrosion resistance of the steel.

(Problem to be Solved by the Invention) By the way, the brazing material that is clad on the surface of the fin in advance contains a large amount of Si component to lower the melting point, and brazing is performed at high temperatures to remove this Si component. This causes a phenomenon in which the fins migrate into the core material of the fins and lower the melting temperature of the fins themselves. Therefore, during brazing, the fins tend to buckle due to the pressure applied by the jig, and this reduces the thickness of the fins. It was an obstacle for me.

On the other hand, from the perspective of anti-corrosion measures for the tube, there are no fins at the bent portion of the tube, and the sacrificial corrosion effect of the fins as mentioned above cannot be expected, so it is necessary to take some kind of anti-corrosion measure for this part. For example, methods such as preparing and attaching a separate plate for sacrificial corrosion or applying a coating material with sacrificial corrosion properties have been considered, but these methods were impractical as they would increase the cost considerably.

As another anti-corrosion measure for tubes, a method has been devised in which the tube surface is subjected to zinc diffusion treatment, but this method has the drawback of requiring the expense of collecting treatment bath waste liquid from beginning to end.

Furthermore, instead of cladding the brazing filler metal for assembly onto the very thin corrugated fins, by cladding the brazing filler metal layer on the side of the tube, which is much thicker than the fins, the melting point of the Si component in the filler metal can be lowered as described above. The inventor of the present invention and others have already attempted a method to avoid the problem of deterioration of fin materials due to the action of fins. In this case, when processing a sheet clad with brazing filler metal into a multi-hole tube shape, some of the brazing filler metal moves inside the holes of the tube, and the brazing between the tube and the fins is sometimes difficult. There were problems such as melting of the brazing material on the inside, reducing the passage area of the hole, and creating a through hole.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a manufacturing method that can reduce the weight of an aluminum heat exchanger and improve its corrosion resistance.

(Means for Solving the Problems) In order to achieve the above objects, the present invention has the following steps: (a) An aluminum tube having a large number of holes is formed by extrusion, and (
c) Bend the tube into a serpentine shape either before or after the Zn-Al alloy coating step, (d) insert an aluminum corrugated fin between the parallel parts of the tube, and (e) A technical means is adopted in which the tube and the corrugated fin are integrally joined through the Zn-A4 alloy layer by heating to the melting temperature of the alloy.

(Function) According to the above technical means, the surface of the extruded multi-hole tube is coated in advance with Zn-Aj! Since the multi-hole tube and the corrugate are joined through the alloy layer, there is no need to clad the corrugated fin with a brazing material made of Al-3i alloy as in the past, and therefore it is possible to increase the Si content when joining the fins. be able to.

Moreover, Zn-Al alloy has a sufficiently high electrode potential compared to tube material, has a sacrificial corrosion effect, and since it is applied over the entire surface of the tube, special post-processing is not required. The corrosion resistance of the tube can be significantly improved without the need for

In addition, Zn-Al alloy has a lower melting point than conventional AA-3t brazing filler metals, so it can be easily coated on the surface of multi-hole tubes by hot-dip plating at relatively low temperatures, improving workability. can do.

(Example) The present invention will be explained below based on embodiments shown in the drawings.

FIG. 1 is a perspective view of a heat exchanger as a condenser for an on-vehicle air conditioner manufactured by the manufacturing method of the present invention, and as seen in the perspective view of FIG. A plurality of partition walls 1a are provided inside and a large number of partition walls 1b are provided inside.
The main component of the heat exchanger is formed by bending the flat tube 1 in a serpentine shape with a predetermined gap, and between the parallel parts of the flat tube 1 there is a very thin wall made of aluminum or aluminum alloy. A corrugated fin 2 for increasing the heat transfer area is inserted, and the tube 1 and fin 2 are made of Zn-Aj?, which has been previously coated on the surface of the tube 1. They are integrally joined by soldering or brazing by the joining force of the alloy layer 3 when it is melted. Vibe joints 4 and 5 are brazed to both open ends of the tube 1 for connection to refrigerant piping.

Next, the manufacturing method of the present invention will be explained step by step. First, a multi-hole flat tube 1 made of aluminum or aluminum alloy and having the above-described cross-sectional shape (see FIG. 2) is molded using an extrusion molding machine. The flat tube 1 is continuously supplied from the left to the right in FIG. 3, and is first fed into a flux coating device A, where a jet pump D coats the surface of the tube with flux 6. Here, as the flux 6, 1nc1. The main component is used.

The tube 1 coated with the flux 6 is then fed into a preheating device B. This preheating device B uses a gas burner E to preheat the tube 1 to a temperature of about 100 to 200°C. Next, the tube 1 is sent to a hot-dip plating apparatus C. In this hot-dip plating apparatus C, Zn is hot-dip plated.
-Heating Al alloy 3゛ above its melting point, Zn-Aj
! Alloy 3" is maintained in a molten state. Here, Zn-
Eutectic component of Al alloy 3゛ (Zn95wt%-Al5wt%
%), its melting point is 382°C.

As a hot-dip plating method, in this example, Zn-A42 is coated on the surface of the tube 1 by passing the tube 1 through a jet of Zn-A6 alloy 3' supplied by a jet pump F.
Melt and peel Alloy 3. The conventionally used Aj!
-Z compared to the melting point (577°C) of the eutectic component of the 3i alloy
Since the melting point of the n-Al alloy 3' can be significantly lowered, it becomes easier to work in the actual manufacturing process and improves workability.

Note that Zn-A42 alloy 3' has a higher melting point when the amount of Zn decreases, reducing the workability of hot-dip plating.
The amount is preferably 60 wt% or more (in the case of 60 wt% Zn, the melting point of the Zn-Al alloy is about 550°C). Here, the Zn-Al alloy 3' is one whose main components are Zn and An, but it goes without saying that it contains some unavoidable impurities, and if necessary, Zn,
Ai! Other appropriate components may be added to some extent.

Figure 4 shows the above Zn-Aj! Figure 3 shows a cross section of tube l coated with alloy 3'. Zn-Am! The tube 1 whose surface is covered with the alloy layer 3 is then bent into a serpentine shape while maintaining a predetermined gap to form the heat exchanger body, and then the fins 2 are inserted between the parallel parts of the tube 1. After fixing and holding with a jig, spray the same flux as used during the hot-dip plating described above to the assembled body of tube 1 and fin 2.

Next, this assembled body is heated in a heating furnace kept at 450° C. to 500° C. for about 10 minutes to melt the Zn-Al alloy layer 3, thereby completing the joining of the tube 1 and the fin 2.

The aforementioned flux is ZnCj! , and is corrosive. Therefore, after the above bonding process is completed, the assembled body is washed with water to remove flux residue.

According to the conventional method of providing a cladding layer of brazing material on the fin surface, the thickness of the corrugated fin 2 is determined by the Si in the brazing material.
It was necessary to maintain a minimum thickness of 0.13 mm due to the above-mentioned buckling strength reduction phenomenon caused by the components, but according to the manufacturing method of the present invention, this type of buckling phenomenon almost never occurs, so the wall thickness Even if thinner fins 2 are used, the fins 2 and tube l can be joined well.

Therefore, when the wall thickness of the fin 2 is varied in the range of 0.16 to 0.06 mm, at what thickness does the buckling phenomenon when joining the fins begin to occur? An experiment was conducted while comparing the method of manufacturing the vessel with the method of the present invention. Table 1 shows the experimental results.

(Left below) Table 1 <Results of fin bonding experiments> As is clear from Table 1, the surface of the fin is clad with brazing filler metal in advance. Whereas buckling would definitely occur if the fin thickness decreased to 0.06 mm or less, in the case of the manufacturing method of the present invention, it was found that buckling only occurred when the fin wall thickness decreased to 0.06 mm or less. It has been demonstrated that the manufacturing method of the present invention greatly helps in reducing the weight of products.

Next, regarding the relationship between the manufacturing method of the heat exchanger and the corrosion resistance of the product, an evaluation test was conducted focusing on the bent portion of the tube 1 where corrosion is most likely to occur, and the results are summarized in Table 2 AB below.

(Leaving space below) Table 2 B Corrosion test results for tubes (conventional product) The numbers for material composition in the above table indicate wt%.

In the test, three types of tube materials were used, and heat exchangers were made using the conventional manufacturing method and the manufacturing method of the present invention.
A corrosion test (cASS test method) specified in DO201 was attempted. As is clear from Table 2 A and B above, products produced using the conventional method started to leak from the bent part of tube 1 300 to 500 hours after the start of the test, regardless of the material of the tube. On the other hand, the manufacturing method of the present invention has no effect on any of the three types of materials tested.
Even after 700 hours, no refrigerant leakage was observed, confirming the excellent corrosion resistance.

Although the above-mentioned embodiment relates to a heat exchanger for an air conditioner installed in an automobile, it goes without saying that the present invention can be similarly applied to various heat exchangers having the same type of structure. Furthermore, in the above embodiment, the Zn-Al alloy 3' is hot-dip plated before the tube 1 is bent into a serpentine shape. - Al alloy 3' may be hot-dip plated.

(Effects of the Invention) As described above, according to the present invention, it is possible to eliminate the phenomenon in which corrugated fins tend to buckle due to the Si component during fin joining, so it is possible to reduce the thickness of the fins.
It is possible to reduce the weight of the heat exchanger.

Moreover, the Zn-Al alloy layer has a sufficiently low electrode potential compared to the tube material, has a sacrificial corrosion effect, and is applied over the entire surface of the tube, so it does not require special post-treatment as in the past. The corrosion resistance of the tube can be significantly improved without requiring any additional steps.

Also, Zn-Aj! The alloy has a lower melting point than conventional Al-3i brazing materials, so it can be easily coated on the surface of a multi-hole tube by hot-dip plating or the like at a relatively low temperature.
Work efficiency can be improved.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a heat exchanger manufactured by the manufacturing method of the present invention, FIG. 2 is a partial cross-sectional perspective view showing the bent shape of the tube in the heat exchanger shown in FIG. 1, and FIG. 3 is a perspective view of the heat exchanger manufactured by the method of the present invention A process outline diagram showing an example of the manufacturing method, FIG. 4, shows Zn-Aj! by the manufacturing method of the present invention. FIG. 2 is a cross-sectional view of a tube coated with an alloy layer. 1...Tube, 2...Fin, 3...Zn-A
1 alloy layer, 3゛...Zn-Al alloy, A... flux coating device, B... preheating device, C... hot-dip plating device. Representative Patent Attorney Takashi Okabe Figure 1 Figure 2

Claims (3)

[Claims] (1) (a) Form an aluminum tube with many holes by extrusion, (b) coat the surface of the tube with Zn-Al alloy, (
c) Bend the tube into a serpentine shape either before or after the Zn-Al alloy coating step, (d) insert an aluminum corrugated fin between the parallel parts of the tube, and (e) A method for manufacturing an aluminum heat exchanger, characterized in that the tube and the corrugated fin are integrally joined via the Zn-Al alloy layer by heating to the melting temperature of the alloy. (2) The method for manufacturing an aluminum heat exchanger according to claim 1, characterized in that the surface of the tube is coated with the Zn-Al alloy by hot-dip plating. (3) Zn content in the Zn-Al alloy is 60w
The method for manufacturing an aluminum heat exchanger according to claim 1 or 2, characterized in that the aluminum heat exchanger is t% or more.